Description

An OpenCL context is created with one or more devices. Contexts are used by the
OpenCL runtime for managing objects such as command-queues, memory, program and kernel
objects and for executing kernels on one or more devices specified in the context.

Parameters

properties

Specifies a list of context property names and
their corresponding values. Each property name is immediately followed
by the corresponding desired value. The list is terminated with 0.
properties can be NULL in which case the platform
that is selected is implementation-defined. The list of supported
properties is described in the table below.

If the extension
cl_khr_dx9_media_sharing
is enabled, then properties specifies a list of context
property names and their corresponding values. Each property is followed
immediately by the corresponding desired value. The list is terminated with
zero. If a property is not specified in properties, then its
default value (listed in the table below) is used (it is said to be specified
implicitly). If properties is NULL or empty (points to
a list whose first value is zero), all attributes take on their default values.

If the extension
cl_khr_d3d10_sharing
is enabled, then properties specifies a list of context
property names and their corresponding values. Each property is followed
immediately by the corresponding desired value. The list is terminated
with zero. if a property is not specified in properties,
then its default value is used (it is said to be specified implicitly). If
properties is NULL or empty (points to a list whose first
value is zero), all attributes take on their default value.

If the extension
cl_khr_gl_sharing
is enabled, then properties points to an attribute list,
which is a array of ordered <attribute name, value> pairs terminated with
zero. If an attribute is not specified in properties,
then its default value is used (it is said to be specified implicitly). If
properties is NULL or empty (points to a list whose first
value is zero), all attributes take on their default values..

Specifies whether the user is responsible for synchronization between OpenCL
and other APIs. Please refer to the specific sections in the OpenCL 1.2 extension specification
that describe sharing with other APIs for restrictions on using this flag.

If CL_CONTEXT_INTEROP_USER_ SYNC is not
specified, a default of CL_FALSE is assumed.

CL_CONTEXT_D3D10_DEVICE_KHR

ID3D10Device*

If the
cl_khr_d3d10_sharing
extension is enabled, specifies the ID3D10Device*
to use for Direct3D 10 interoperability. The default value is NULL.

CL_GL_CONTEXT_KHR

0, OpenGL context handle

OpenGL context to associated
the OpenCL context with (available if the
cl_khr_gl_sharing
extension is enabled)

CL_EGL_DISPLAY_KHR

EGL_NO_DISPLAY, EGLDisplay handle

EGLDisplay an OpenGL context was
created with respect to (available if the
cl_khr_gl_sharing
extension is enabled)

CL_GLX_DISPLAY_KHR

None, X handle

X Display an OpenGL context was
created with respect to (available if the
cl_khr_gl_sharing
extension is enabled)

CL_CGL_SHAREGROUP_KHR

0, CGL share group handle

CGL share group to associate the OpenCL context with (available if the
cl_khr_gl_sharing
extension is enabled)

CL_WGL_HDC_KHR

0, HDC handle

HDC an OpenGL context was created with respect to (available if the
cl_khr_gl_sharing
extension is enabled)

A callback function that can be registered by the application. This callback
function will be used by the OpenCL implementation to report information
on errors during context creation as well as errors that occur at runtime
in this context. This callback function may be called asynchronously by
the OpenCL implementation. It is the application's responsibility to ensure
that the callback function is thread-safe. If pfn_notify
is NULL, no callback function is registered. The parameters to this callback
function are:

errinfo is a pointer to an error string.

private_info and cb represent a pointer
to binary data that is returned by the OpenCL implementation that can be used
to log additional information helpful in debugging the error.

user_data is a pointer to user supplied data.

NOTE: There are a number of cases where error notifications need to be
delivered due to an error that occurs outside a context. Such notifications
may not be delivered through the pfn_notify callback. Where
these notifications go is implementation-defined.

user_data

Passed as the user_data argument when
pfn_notify is called. user_data can
be NULL.

errcode_ret

Returns an appropriate error code. If errcode_ret is NULL,
no error code is returned.

Notes

clCreateContext and
clCreateContextFromType
perform an implicit retain. This is very helpful for 3rd party libraries, which
typically get a context passed to them by the application. However, it is possible
that the application may delete the context without informing the library. Allowing
functions to attach to (i.e. retain) and release a context solves the problem of a
context being used by a library no longer being valid.

Errors

clCreateContext returns a valid non-zero context and
errcode_ret is set to CL_SUCCESS if the
context is created successfully. Otherwise, it returns NULL value with the following
error values returned in errcode_ret:

CL_INVALID_PLATFORM if properties
is NULL and no platform could be selected or if platform value specified
in properties is not a valid platform. (If the extension
cl_khr_gl_sharing
is enabled, then this error is replaced with
CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR; see below.)

CL_INVALID_PROPERTY if context property name in
properties is not a supported property name, if the
value specified for a supported property name is not valid, or if the
same property name is specified more than once. However if the extension
cl_khr_gl_sharing is
enabled, then CL_INVALID_PROPERTY is returned if an attribute
name other than those listed in the table for properties
above or if CL_CONTEXT_INTEROP_USER_SYNC is specified in
properties.

CL_INVALID_PROPERTY if an attribute name other than those
specified in table 4.5 or if CL_CONTEXT_INTEROP_USER_SYNC is
specified in properties.

CL_INVALID_VALUE if devices is NULL; if
num_devices is equal to zero; or if pfn_notify
is NULL but user_data is not NULL.

CL_INVALID_DEVICE if devices contains an invalid device.

CL_INVALID_OPERATION if Direct3D 10 interoperability is
specified by setting CL_INVALID_D3D10_DEVICE_KHR to a non-NULL
value, and interoperability with another graphics API is also specified (if the
cl_khr_d3d10_sharing
extension is enabled).

CL_DEVICE_NOT_AVAILABLE if a device in devices
is currently not available even though the device was returned by
clGetDeviceIDs.

CL_OUT_OF_RESOURCES if there is a failure to allocate resources
required by the OpenCL implementation on the device.

CL_OUT_OF_HOST_MEMORY if there is a failure to allocate
resources required by the OpenCL implementation on the host.

CL_INVALID_D3D10_DEVICE_KHR if the Direct3D
10 device specified for interoperability is not compatible with
the devices against which the context is to be created (if the
cl_khr_d3d10_sharing
extension is enabled).

CL_INVALID_D3D10_DEVICE_KHR if the value of the property
CL_CONTEXT_D3D10_DEVICE_KHR is non-NULL and does not specify
a valid Direct3D 10 device with which the cl_device_ids
against which this context is to be created may interoperate (if the
cl_khr_d3d10_sharing
extension is enabled).

CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR when an invalid OpenGL
context or share group object handle is specified in properties (only
if the cl_khr_gl_sharing
extension is enabled).

CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR if no OpenGL or
OpenGL ES context or share group is specified in the attribute list given to
clCreateContext
and any of the commands in section 9.7 are called. (if the
cl_khr_gl_sharing extension
is enabled)

CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR if the
cl_khr_gl_sharing
extension is enabled and if a context was specified by any of the following means:

A context specified for an EGL-based OpenGL ES or OpenGL implementation
by setting the attributes CL_GL_CONTEXT_KHR and
CL_EGL_DISPLAY_KHR.

A context was specified for a GLX-based OpenGL implementation by
setting the attributes CL_GL_CONTEXT_KHR and
CL_GLX_DISPLAY_KHR.

A context was specified for a WGL-based OpenGL implementation by
setting the attributes CL_GL_CONTEXT_KHR and
CL_WGL_HDC_KHR.

and any of the following conditions hold:

The specified display and context attributes do not identify a valid
OpenGL or OpenGL ES context.

The specified context does not support buffer and renderbuffer objects.

The specified context is not compatible with the OpenCL context being
created (for example, it exists in a physically distinct address space,
such as another hardware device, or does not support sharing data with
OpenCL due to implementation restrictions).

CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR if a
share group was specified for a CGL-based OpenGL implementation by
setting the attribute CL_CGL_SHAREGROUP_KHR, and the
specified share group does not identify a valid CGL share group object (if the
cl_khr_gl_sharing extension
is enabled).

CL_INVALID_OPERATION if a context was specified as described above
and any of the following conditions hold:

A context or share group object was specified for one of CGL, EGL, GLX, or WGL
and the OpenGL implementation does not support that window-system binding API.

More than one of the attributes CL_CGL_SHAREGROUP_KHR,
CL_EGL_DISPLAY_KHR, CL_GLX_DISPLAY_KHR,
and CL_WGL_HDC_KHR is set to a non-default value.

Both of the attributes CL_CGL_SHAREGROUP_KHR and
CL_GL_CONTEXT_KHR are set to non-default values.

Any of the devices specified in the devices argument cannot support OpenCL
objects which share the data store of an OpenGL object, as described in
section 9.7.

CL_INVALID_DX9_MEDIA_ADAPTER_KHR if the
media adapter specified for interoperability is not compatible with
the devices against which the context is to be created (only if the
cl_khr_dx9_media_sharing
extension is supported).

CL_INVALID_ADAPTER_KHR if
any of the values of the properties CL_CONTEXT_ADAPTER_D3D9_KHR,
CL_CONTEXT_ADAPTER_D3D9EX_KHR or
CL_CONTEXT_ADAPTER_DXVA_KHR is non-NULL and
does not specify a valid media adapter with which the cl_device_ids
against which this context is to be created may interoperate (only if the
cl_khr_dx9_media_sharing
extension is supported).

CL_INVALID_OPERATION if interoperability is
specified by setting CL_CONTEXT_ADAPTER_D3D9_KHR,
CL_CONTEXT_ADAPTER_D3D9EX_KHR or
CL_CONTEXT_ADAPTER_DXVA_KHR to a non-NULL value, and
interoperability with another graphics API is also specified (only if the
cl_khr_dx9_media_sharing
extension is supported).

CL_INVALID_OPERATION
if Direct3D 11 interoperability is specified by setting
CL_INVALID_D3D11_DEVICE_KHR to a non-NULL value, and
interoperability with another graphics API is also specified (only if the
cl_khr_d3d11_sharing
extension is supported).

CL_INVALID_D3D11_DEVICE_KHR if the value of the property
CL_CONTEXT_D3D11_DEVICE_KHR is non-NULL and does not specify
a valid Direct3D 11 device with which the cl_device_ids
against which this context is to be created may interoperate (only if the
cl_khr_d3d11_sharing
extension is supported).

CL_INVALID_D3D11_DEVICE_KHR if the Direct3D
11 device specified for interoperability is not compatible with
the devices against which the context is to be created (only if the
cl_khr_d3d11_sharing
extension is supported).